Paul Ormerod is an economist at Volterra Partners, a visiting professor at University College, London, and author of Positive Linking: How Networks can Revolutionise the World.

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Digital comparison tools save time and effort for people by making searches and comparisons easier (Source: Getty)

Paul Ormerod

The competition and Markets Authority (CMA) published a report about Price comparison sites at the end of last month. They seem simple enough, but these straightforward sites raise interesting issues for economics.

Overall, the CMA was pretty positive about the DCTs – digital comparison tools, to give them their Sunday best name. The conclusion was that “they make it easier for people to shop around, and improve competition – which is a spur to lower prices, higher quality, innovation and efficiency”.

DCTs offer two main benefits. First, they save time and effort for people by making searches and comparisons easier. Second, they make suppliers compete harder to provide lower prices and better choices to consumers. In short, they bring the real world closer to the perfectly informed consumers and perfectly competing firms in the ideal world of economic theory.

But even in this market, there is an issue which goes right to the heart of much of the information which can be accessed through the internet: how do we know whether we can trust it?

The main problem is that the comparison sites typically provide their services free of charge to consumers. They make money by charging a commission to suppliers.

This creates an incentive for a DCT to promote those suppliers which pay it the most commission. An effective way of doing this on the internet is by the order in which the information on the various suppliers is presented.

It is not that DCTs deliberately provide misleading information, or even that a site leaves off a major supplier which does not pay the particular website enough. But they can put those that pay the most at the top of the list.

Notoriously with Google searches, people rarely click through to anything which is not in the top three results of the search.

Allegedly, 60 per cent of the time, only the site which comes at the very top of is accessed.

Obviously on a DCT, consumers are likely to look at more. That is the whole point of using the site. But although the CMA does not provide hard data on this, it expresses a clear concern about the ways in which the sites rank the suppliers.

How the DCTs themselves set their prices raises a more general question for economics. The basic rule, described in the textbooks since time immemorial, is to set price equal to marginal cost – in other words, at the point where the revenue from one extra sale equals the cost of producing that extra item.

The standard assumption made in teaching generations of students their introductory course to economics is that as the level of output increases, marginal cost first of all falls but eventually rises.

But on the internet, once the site is set up, the cost of dealing with an extra user is effectively zero. The time-hallowed formula of economics is a recipe for bankruptcy.

The internet is forcing companies to innovate in their pricing strategies. And it is forcing economists to rethink some of their theories.